This invention relates to cathode ray tubes for projection television, and more particularly relates to a spring contactor for electrically bridging the frit seal between the panel and funnel portions, and also relates to a projection tube employing such a spring contactor.
Commercial color television projection systems in general rely upon the superimposing of three different video images on the projection screen, each image in one of the primary colors red, blue or green, in order to reproduce a full color video image. In such a system the video signals for each of the primary colors are fed to separate monochrome cathode ray tubes whose display screens are each comprised of a phosphor emitting in one of the primary colors. The monochrome video images formed on the tube display screens are then projected through suitable projection optics onto the rear surface of a rear projection screen for display to an audience.
In such color television projection systems a number of problems occur. For example, the projection of a flat display on a flat projection screen requires a complicated system of lenses, 5 to 8 element lenses typically being necessary for optical quality. Moreover, despite such complex lens systems, a brightness decline of approximately 20 percent generally occurs from the center to the corners of the projection screen. In addition, the overall brightness of the projection screen is generally less than desired. Choosing phosphors based on their superior brightnesses of emission has unfortunately resulted in other problems, such as inferior color rendition and chromatic abberation.
By providing the projection television display tubes with a curved display screen including a multi-layer intereference filter, these problems are solved for the greater part. See for example U.S. Pat. No. 4,683,398, issued July 28, 1987 to Vriens et al. For ease of manufacturing, such tubes are produced in two parts, a face panel and a funnel, which parts are frit sealed together in a manner similar to the conventional frit sealing of color cathode ray tubes for direct view color television. Such a two-part construction enables easier fabrication of a face panel having the necessary curvature and interference filter.
Subsequent to formation of the interference filter on the curved display screen surface, a monochrome phosphor layer is deposited on the filter, such as by settling of phosphor particles from a slurry. Following deposition of the phosphor layer, a thin evaporated aluminum layer is formed over the phosphor layer in the conventional manner.
In order to provide anode potential to the screen, electrical contact must be provided between the aluminum layer and the anode button located in the sidewall of the funnel portion of the tube. In FIG. 2 of British Pat. No. 2,075,748, a projection tube is shown in which the necessary electrical contact is provided by a spring contactor 15, having one end attached to the anode button 14 and the other end free to resiliently contact conductive layer 13 (e.g., evaporated aluminum) on the inner surface of the panel 12.
Problems encountered in attaching the spring contactor to the anode button include the production of loose particles, a notorious source of defects in such high voltage cathode ray tubes. Such loose particles can, for example, become lodged on parts of the high voltage electron gun, causing shorting and/or arcing.
One source of particles is weld splatter occurring during the welding of the contactor to the anode button. In order to avoid this problem, it has been proposed to mechanically attach the contactor to the anode button. One means for mechanical attachment is shown in U.S. Pat. No. 4,230,966, issued Oct. 28, 1980, to J. Compen. In this patent, a contactor comprises an elongated strip of spring material, having a U-shaped portion at each end of the strip for making slidable contact with the interior conductive coating of the funnel and having a keyhole-shaped aperture in the middle of the strip which may be slidably engaged with a stud upstanding on the anode button. During insertion and attachment of the strip to the anode, the strip is downwardly flexed to engage the anode button stud in the large portion of the aperture, and then laterally slide the strip along the internal coating until the stud is secured in the small portion of the aperture.
A similar arrangement when tried in a projection cathode ray tube was found to produce loose particles through the frictional engagement of the contact member with the internal coating during insertion and engagement with the anode button stud, due to the necessity for downward flexing of the spring member against the coating while at the same time laterally sliding the member in order to engage the stud.
Accordingly, it is an object of the invention to provide an internal spring contactor for a projection cathode ray tube which may be conveniently mechanically attached to the stud of an anode button while substantially avoiding frictional contact with the internal conductive coating on the funnel of the tube.